A lithography technique is used to form a desired circuit pattern in a semiconductor device. In the lithography technique, patterns using an original picture pattern called reticle (which is referred to as mask as well, and hereafter referred to generally as “reticle”) are transferred. At this time, an electron beam (electron ray) drawing technique having an excellent resolution is used to manufacture a high precision reticle.
As the electron beam (electron ray) drawing technique, for example, there is a drawing device using multi-beams. As compared with the case where a single electron beam is used for the drawing, the reticle can be irradiated with a large number of beams at one time by using the multi-beams. As a result, the throughput for fabricating the reticle can be improved remarkably.
In a drawing device of such a multi-beam system, for example, an electron beam emitted from an electron gun passes through an aperture member having a plurality of holes to form multi-beams. Each of the formed multi-beams is subject to blanking control. Multi-beams that are not shielded are zoomed out by an optical system, and deflected by a deflector. The deflected multi-beams are irradiated on a sample.
For securing a drawing precision, it is necessary to properly calibrate (correct) a current quantity of an electron beam. For example, in a single beam system, especially in a variable shaping system, the shot size changes by each shot. Therefore, it is suitable to adjust the current density of the electron beam so as to be uniform. On the other hand, in the multi-beam system, the shot size of the individual electron beam is fixed to the same size without conducting variable shaping unlike the single beam system. Therefore, in the multi-beam system, it becomes necessary to adjust the current quantity of each electron beam so as to be uniform.
Furthermore, in the single beam system, an area cut out as a shot from the electron beam emitted from the electron gun is small. Therefore, it is possible to make the current density in the area nearly uniform. In the multi-beam system, however, a large number of beams are cut out from a wide area. Therefore, it is difficult to implement uniformity of the current in respective currents. Therefore, it is necessary to correct the irradiation time depending on variation of current quantity in individual multi-beams.
In the case where the current quantity of the electron beam is measured, the measurement is conducted by utilizing a Faraday cup in both the single beam system and the multi-beam system described above.
In prior-art, however, the following points are not considered.
That is, when measuring the current quantity of the electron beam, especially in the case of the multi-beam system, the number of electron beams becomes enormous and consequently the current quantity of each electron beam to be measured cannot help becoming very minute. That is, in the case of the multi-beam system, the current quantity of an electron beam that has passed through each aperture hole formed through the aperture member is, for example, approximately 2 pA. After the electron beam is received by the Faraday cup, the current quantity of the electron beam is measured.
Considering that the precision demanded for the measured current quantity is for example, approximately 0.1% with respect to the setting, a micro-ammeter having a resolution of at least 0.1% of the input electron beam, i.e., 2 fA is needed.
If the resolution is 2 fA, however, noise at the time of measurement is large and it is difficult to conduct effective measurement even if a micro-ammeter is used.
Furthermore, since it is difficult to measure a minute current, it is also conceivable to, irradiate, for example, a silicon diode or the like directly with an electron beam, amplify a current, and measure the amplified current.
As the measurement is continued, however, the amplification factor is degraded. Inevitably, an individual difference of the resolution or the like of every measurement system occurs. It cannot be dissolved completely. Therefore, it is difficult to measure the absolute value of current quantity of a minute electron beam accurately with a resolution of, for example, fA order.